The present invention relates to a network system having a plurality of nodes (circuit switches, packet switches, and the like) connected to a public switched network (a public electronics and communication service network such as a public switched telephone network, Integrated Services Digital Network (ISDN), and the like). More particularly, the present invention relates to a method and apparatus for the network system for providing data transfer services to a subscriber, and a method and apparatus for connecting a circuit between nodes in the network system.
For transferring data, e.g., speech by using a public switched network, there are known a transfer function of an automatic answering telephone set and so called a variable absence transfer function of a private branch exchange. According to the transfer function of an automatic answering telephone set, after a call is once received by an automatic answering telephone set (after the automatic answering telephone set responds to an external call), the telephone set transfers the call to a transfer destination previously registered, by all means irrespective of the contents of the call. According to the variable absence transfer function, a private branch exchange transfers a call to a transfer destination previously registered, by all means irrespective of who made the call. A toll for speech transfer is charged to both a subscriber sending a message (a subscriber wanting to make speech transfer) and a subscriber receiving the message (a subscriber receiving the transferred message).
The techniques of this type are described, for example, in "New Telephone Ages" by Mitsuru SUGAYA, published by Kabushiki Kaisha Data House (hereinafter called Document (1)).
For a network system having a plurality of nodes connected to a public switched network, there is known a storage type data transfer method described, for example, in Japanese Patent Laid-open Publication JP-A 57-131148 (herein after called Document (2)). According to this method, when data to be transferred is generated at a terminal equipment at a transfer deliverer node, this data is temporarily stored in a data file of this node. The transfer deliverer node sends a notice to a terminal equipment at a transfer destination node, the notice indicating that the data to be transferred has been stored. Upon reception of this notice, the terminal equipment requests the data exchange to transmit the data stored in the data file, and receives the transferred data.
The convention technique described in Document (1) does not consider a security function of a speech transfer unit (an automatic answering telephone set, a private branch exchange, and the like) for preventing and unauthorized access by identifying a subscriber wishing to receive a service of speech transfer. Therefore, the speech transfer unit supplies a speech transfer service to all types of speeches even by an unauthorized access. In addition, it does not consider a toll control function. Therefore, it is associated with the problem that a toll for speech transfer is charged to both a subscriber sending a speech and a subscriber receiving the transferred speech.
With the conventional technique described in Document (2), each time transfer data is generated, the data is temporarily stored in a data file at the transfer delivered node. A notice to this effect is sent to a transfer destination node. Upon reception of a transfer request from the transfer destination node, the node sets a circuit to transfer the data. After the data transfer, the circuit is disconnected. According to a toll system of a public switched network, a transfer fee is charged by each unit time. Therefore, if it takes, for example 3 minutes and 10 seconds to transfer data, assuming that the unit time is 3 minutes for example, the circuit is held for 6 minutes and the transfer fee for 6 minutes is charged. In other words, during the remaining 2 minutes and 50 seconds while the circuit is held, this circuit is not efficiently used.